This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present invention, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Development of safe and effective immunotherapies for human use remains an urgent medical need for patients worldwide. In order to elicit appropriate immune responses, immunologic modifiers (“immunomodifiers”) that enhance, direct, or promote an immune response can be used in vaccine design or immunotherapy [Gregoriadis, G., Immunological adjuvants: a role for liposomes. Immunol Today 11:89 (1990)]. For example, vaccines may include antigens to stimulate an immune response. However, some potential vaccines that include antigens are weak stimulators of an immune response because the vaccines do not efficiently deliver the antigen to antigen presenting cells (“APC”) of the immune system and/or the antigen is weakly immunogenic. Thus, immunotherapies that effectively deliver antigens to APC, and also stimulate the immune system to respond to the antigen, are needed. Immunomodifiers have the potential to function as such an immunotherapy. Such immunotherapies may have these and other benefits. For example, when included as part of a therapeutic vaccine, an immunomodifier should at least (1) improve antigen delivery and/or processing in the APC [Wang, R. F., and Wang, H. Y. Enhancement of antitumor immunity by prolonging antigen presentation on dendritic cells. Nat Biotechnol 20:149 (2002)], (2) induce the production of immunomodulatory cytokines that favor the development of immune responses to the vaccine antigen, thus promoting cell mediated immunity, including cytotoxic T-lymphocytes (“CTL”), (3) reduce the number of immunizations or the amount of antigen required for an effective vaccine [Vogel, F. R. Improving vaccine performance with adjuvants. Clin Infect Dis 30 Suppl 3:S266 (2000)], (4) increase the biological or immunological half-life of the vaccine antigen, and (5) overcome immune tolerance to antigen by inhibiting immune suppressive factors [Baecher-Allan, C., and Anderson, D. E. Immune regulation in tumor-bearing hosts. Curr Opin Immunol 18:214 (2006)].
Presently, the primary class of agents used to enhance the efficacy of antigens, such as peptide or protein antigens, in eliciting an immune response are adjuvants such as water-in-oil emulsions, alum, and other chemicals which enhance antigen responses; however, these adjuvants are not immunomodifiers, as described above, because they have no direct immunomodulatory effects themselves [Vogel, F. R., and Powell, M. F. A compendium of vaccine adjuvants and excipients, Pharm Biotechnol 6:141 (1995)]. Several such adjuvants are available for use in animals and some of them have been tested in clinical trials. In addition to traditional adjuvants such as the aluminum salts, products such as influenza virosomes [Gluck, R., and Walti, E. 2000. Biophysical validation of Epaxal Berna, a hepatitis A vaccine adjuvanted with immunopotentiating reconstituted influenza virosomes (IRIV). Dev Biol (Basel) 103:189 (2000)] and Chiron's MF59 [Kahn, J. O., et al. Clinical and immunologic responses to human immunodeficiency virus (HIV) type 1SF2 gp120 subunit vaccine combined with MF59 adjuvant with or without muramyl tripeptide dipalmitoyl phosphatidylethanolamine in non-HIV-infected human volunteers. J Infect Dis 170:1288 (1994)], which have intrinsic immune effects, are being marketed. For example, MF59, which is a submicron emulsion based adjuvant, is internalized by dendritic cells [Dupuis, M., et al., Dendritic cells internalize vaccine adjuvant after intramuscular injection. Cell Immunol 186:18 (1998)]. However, according to clinical trial reports on HSV and influenza vaccines [Jones, C. A., and Cunningham, A. L. Vaccination strategies to prevent genital herpes and neonatal herpes simplex virus (HSV) disease. Herpes 11:12 (2004); Minutello, M. et al., Safety and immunogenicity of an inactivated subunit influenza virus vaccine combined with MF59 adjuvant emulsion in elderly subjects, immunized for three consecutive influenza seasons. Vaccine 17:99 (1999)], evidence from animal models suggests that the MF59 adjuvant enhances production of neutralizing antibodies rather than enhancing T-cell responses. Thus new methods of stimulating cell mediated immune responses are needed.
Further, as mentioned above, some antigens are weak stimulators of an immune response. Thus, in addition to co-administering antigen with substances that stimulate immune responses, as described above, a weakly immunogenic antigen can be modified to increase its immunogenicity. For example, a weakly immunogenic antigen can be coupled to immunogenic peptides, polysaccharides, or lipids to increase its immunogenicity. However, simply coupling weakly immunogenic antigens to these types of compounds may not be sufficient to elicit an immune response. For example, the resulting immune response may be directed to immunogenic epitopes on the coupled compound and not the weak antigen, or the coupled antigen may not be efficiently delivered APC of the immune system. Thus, additional methods are needed to stimulate immune responses to antigens that are weakly immunogenic.